1. Field of the Invention
This invention relates in general to process for producing inversely operated transistors in a semiconductor body.
2. Description of the Prior Art
In transistors the charge carriers injected from the emitter zone diffuse through the base zone to the collector zone. This process can be accelerated by an internal electric field in the base zone which is called the "drift field". The magnitude of the drift speed of a charge carrier is proportional to the degree of the field strength. In the case of an electron the acceleration takes place in a direction opposite to the field direction whereas in the case of a positive hole it takes place in the field direction.
In transistors produced by the conventional planar technique by the diffusion process result in doping gradients in the base zone which cause drift fields that drive injected carrier charges from the surface zone of the semiconductor body into the interior of the semiconductor body. In a normally operated transistor the injected charged carriers are accelerated from the emitter zone to the collector zone. On the other hand in the case of an inversely operated transistor such as in the case of a transistor in the so-called "MTL or I.sup.2 L technique" (Merged-Transistor-Logic, and Integrated-Injection-Logic), the drift field produces a deceleration of the diffusing charge carriers as the injected charge carriers are diffused from the interior of the semiconductor body towards its surface. The result is an increase in base transit time and, thus, a possible reduction in switching speeds.